Toroidal transmission

ABSTRACT

A roller transmission, in particular toroidal transmission, with infinitely variable transmission ratio, includes a friction wheel ( 6 ) disposed between a driving disk ( 2 ) and driven disk ( 3 ) and rotatably mounted to a swingable carrier ( 7 ). The friction wheel has a circumferential friction surface ( 8 ) for interaction with confronting end faces ( 4, 5 ) of both disks ( 2, 3 ). The friction wheel ( 6 ) is made of two sheet metal parts ( 9, 10 ) interconnected outside the friction surface ( 8 ) and defining a partition plane which is disposed substantially transversely to the rotation axis of the friction wheel ( 6 ), wherein at least one cavity ( 15 ) is arranged between both sheet metal parts ( 9, 10 ).

The present invention relates to a roller transmission, in particulartoroidal transmission, with infinitely variable transmission ratio.Transmissions of this type can be installed in motor vehicles to replaceconventional manually shifted transmissions or automatic transmissionswith torque converter.

BACKGROUND OF THE INVENTION

European Pat. No. EP 0528383-B discloses, for example, a infinitelyvariable toroidal transmission which has a driving disk and a drivendisk in coaxial relationship. A friction wheel is positioned betweenboth disks and has a peripheral friction surface for interaction withconfronting end faces of both disks. Power is transmitted from thedriving disk onto the friction wheel and from the friction wheel to thedriven disk via a traction fluid. The traction fluid acts between thefriction surface of the friction wheel and the end faces of the disks.The friction wheel is rotatably supported by a swingable carrier.Friction wheel, driving disk and driven disk are massive componentswhich must have an extraordinarily high stiffness as the friction wheelis clamped between both disks at a pressure of about 12 tons. Thispressure load is required to reliably transmit the circumferentialforces, transmitted through frictional engagement, from the drive to theoutput. Roller transmissions of this type are characterized by arelatively high own weight which runs counter to the demand by theautomobile industry for light constructions.

European Pat. No. EP 0 283 855-A1 describes a toroidal transmissionhaving a friction wheel which is of lighter weight compared to theafore-described friction wheel as a consequence of its thin-walledconfiguration. However, thin-wall friction disks run the risk ofbuckling when exposed to high loads. The friction disk has a continuouscircumferential collar for contacting the driving disk and the drivendisk. This collar is not supported at its axial ends and thus can evadea radial load.

U.S. Pat. No. 1,175,667-A describes a toroidal transmission having afriction disk with a cavity for reducing the weight of the frictiondisk; the cavity is provided for receiving a lubricant which can exitthrough oil channels in order to lubricate the bearing of the frictiondisk and its shaft. In addition, a type of tire is attached to thefriction disk for interaction with the driveshaft and the driven shaft.The tire represents an additional component which has to be attachedthrough an additional working step.

OBJECT OF THE INVENTION

It is thus an object of the present invention to provide a rollertransmission, having a reduced own weight while maintaining the requiredstiffness and being composed of a reduced number of single components.

SUMMARY OF THE INVENTION

In accordance with the invention, this object is attained by forming thefriction wheel of two sheet metal parts interconnected outside thefriction surface and defining a partition plane which is arrangedsubstantially transversely to the rotation axis of the friction wheel,with at least one cavity disposed between both sheet metal parts. Thecavity or cavities significantly reduce the weight of the toroidaltransmission according to the invention. The cavity or cavities are sospaced about the perimeter of the friction wheel that the friction wheelturns reliably without unbalance. The cavity or cavities may becompletely encompassed by both sheet metal parts, for example, in orderto preclude an ingress of traction fluid into the cavities. The cavitiesmay, however, also communicate with the surroundings of the frictionwheel. The friction surface may be provided, for example, on acircumscribing collar of one of the sheet metal parts; No separate tireis then required. As a consequence of the interconnection of the sheetmetal parts outside the friction surface, it is ensured that no buttedges are encountered in the area of the friction surface. Both sheetmetal parts are so matched to one another that the collar issufficiently supported on both axial ends but is prevented from freelyjutting out, as this is the case, for example, with the fiction diskaccording to European Pat. No. EP 0 283 855.

The outer configuration of the friction wheel in relation to themassively shaped friction wheels may be substantially maintained. Theaxial extension of the friction wheels and the wall thickness of thesheet metal parts may be so sized that, on the one hand, a sufficientlylarge contact area of the friction wheel is ensured, and, on the otherhand, a sufficient stiffness of the friction wheel is guaranteed at theradial pressure of about 12 tons. The friction wheel may be, optionally,further extended in axial direction to meet these conditions, wherebythe volume of the cavity, bounded by the sheet metal parts, increases.

A further advantageous effect of the roller transmission according tothe invention resides in the reduction of the adjusting forces foradjusting the friction wheels, as will be described hereinafter. Amodification of the transmission ratio between drive and output—forexample, to increase the output speed—is implemented by so tilting thecarrier of the friction wheel that the friction surface bears, on theone hand, upon the driving disk radially further outwards, and, on theother hand, upon the driven disk radially further inwards. This meansthat the rotation axis of the rotating friction wheel is tilted duringthis adjustment. This adjustment of the rotation axis generates,however, undesired centrifugal forces which may render an adjustmentmovement more difficult. These centrifugal forces are dependent on themass of the friction wheel, on the one hand, and on the speed of thefriction wheel, on the other hand. As a consequence of the reduced massof the friction wheels made of sheet metal, significantly reducedcentrifugal forces are produced so that the adjustment of the frictionwheels can be realized in a more simple manner.

A further advantage is the significantly lower costs for manufacturingthe friction wheels of sheet metal compared to manufacturing costs formassive friction wheels which have to be machined in any event.

Oftentimes, the surface area of the friction wheel is convexly curved.Therefore, the confronting end faces of the driving disk and driven diskare concavely curved so that a reliable contact of the friction surfaceupon the end faces of both disks is ensured regardless of the positionof the carrier. In order to provide a convex shape, the surface area ofconventional massive friction wheels must be grinded. Grinding of theconvex friction surface requires, however, particular care. When thesurface area is grinded from both end faces inwardly, there is a riskthat approximately in the axial center a circumferential edge is formedwhich can be seen by the naked eye only very difficult. Such edges may,however, cause the friction wheel to no longer run reliably duringoperation because the traction fluid can no longer reliably transmit theforces; Thus, inadmissibly high compression may be encountered in thearea of the circumferential edge that may lead to a total breakdown ofthe friction wheel. Through the provision of the toroidal transmissionaccording to the present invention, it is now possible to form theconvex friction surface by way of a non-cutting process onto thedisk-shaped sheet metal parts, without causing formation of such anedge.

Particular consideration should be directed to the interconnection ofboth sheet metal parts, when taking into account especially the greatcontact pressure forces. On the one hand, the operation of the frictionsurface should not be impaired by the interconnection of both sheetmetal parts, while, on the other hand, care should be taken that theforce flow in the friction wheel does not inadmissibly strain theinterconnection. According to a further development of the invention, itis provided to weld together both sheet metal parts, with the weldingseam located outside the friction surface. A welded connection oranother connection can be realized in a particularly easy manner whenthe one disk-shaped sheet metal part is formed in one piece on its outerperimeter with a circumferential outer collar having an outer surfacearea defining the friction surface, whereas the other disk-shaped sheetmetal is arranged within the outer collar and securely fixed—preferablyby a welded connection—to the inner surface area of the outer collar.Both disk-shaped sheet metal parts may have substantially flat end facesso as to define therebetween a cavity bounded by the axial dimension ofthe collar. The other sheet metal part is suitably so disposed as tobear against the outer edge of the free end of the collar. In thismanner, a deflection of the free end of the collar as a result of a highpressure load is precluded. As both sheet metal parts are substantiallyof flat configuration, the friction wheel according to the invention isnot exposed or only slight exposed to a bending stress or shearingstress.

The outer surface area of the collar is convexly curved for formation ofthe friction surface. As already stated further above, the convexcurvature on the collar of the one sheet metal part can be produced byshaping through a rolling process to impart the outer peripheral surfaceof the collar with the desired convex curvature. Other shaping processesare, however, also conceivable, for example the deep-drawing process.Should it be required, it is, of course, possible to later finish theouter surface area of the collar through a grinding process to producethe convex curvature or to optimize the already shaped convex surfacearea.

According to a further, particularly suitable, further development ofthe invention, the friction wheel is provided with a coaxial innercollar. This collar may be provided on both end faces of the frictionwheel and project axially out. The collar may also be disposed axiallyinwards of the friction wheel.

Referring back to the exemplified embodiment, mentioned already above,with two disk-shaped sheet metal parts, the operation of the collar willnow be described in more detail. The free ends of both inner collars maycon front one another, with both collars demarcating together a hubopening for receiving a bolt which is in fixed rotative engagement withboth sheet metal parts. This bolt may then be supported, e.g. by arolling-contact bearing, upon the swingable carrier. In this case, theinner collars are arranged, preferably, within the axial extension ofthe sheet metal parts of substantially flat configuration.

The free end of both inner collars may, however, also be facing awayfrom one another, whereby respective radial bearings are disposedbetween both inner collars and the carrier. No bolt is provided in thisvariation of the invention. The friction wheel may be supported directlyby the carrier at interposition of the radial bearing. In this manner, afurther reduction of mass is realized by the rolling transmissionaccording to the invention.

In the preceding variation of the invention, the outer surface area ofthe inner collar may be formed for rolling bodies with a raceway, forexample as ball groove, in the outer surface area. Therefore, theprovision of a separate bearing race, for example for a radial deepgroove ball bearing, is no longer necessary.

It may be required or suitable to provide at least one of both sheetmetal parts with several depressions spaced about the circumference andjutting out in the direction of the other sheet metal part forsignificantly increasing the stiffness of the friction disk according tothe invention. The depressions may, for example, jut out to such anextent as to bear upon the opposite sheet metal part. The depressionsmay be securely fixed in the area of contact with the other sheet metal,for example by spot welding. In this manner, the stiffness of thefriction wheel is further enhanced. The support of the opposite sheetmetal part upon the depressions prevents a buckling of the sheet metalpart when exposed to the great radial load. Of course, both sheet metalparts may be provided with such depressions.

BRIEF DESCRIPTION OF THE DRAWINGS

Two exemplified embodiments of the invention will now be described withreference to a total of four figures, in which:

FIG. 1 is a longitudinal section of one half of a friction wheelaccording to the invention,

FIG. 1a shows a fragmentary sectional section of a modified embodimentof a friction wheel according to the invention.

FIG. 2 is a schematic longitudinal section of a conventional toroidaltransmission;

FIG. 3 is a longitudinal section of one half of another friction wheelaccording to the invention; and

FIG. 4 is a top view of the friction wheel according to the inventionshown in FIG. 3.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a longitudinal section of a friction wheel according to theinvention for use in a conventional toroidal transmission, as shownschematically in FIG. 2. Mounted on a driveshaft 1 are driving disks 2and driven disks 3. The driving disks 2 are mounted in fixed rotativeengagement with the driveshaft 1. The driven shafts 3 are positionedbetween both driving disks 2 and supported for rotation relative to thedriveshaft 1. Confronting end faces of the neighboring driving disks 2and driven disks 3 are provided with concavely curved contact surfaces4, 5 for friction wheels 6. The friction wheels 6 are rotatably mountedto swingable carriers 7. About their circumference, the friction wheels6 are provided with convex friction surfaces 8 which are pressed againstthe contact surfaces 4, 5. The driven disks 3 are mounted in fixedrotative engagement with a toothed ring 9 for attachment of furthertransmission components (not shown).

The friction wheel 6 is made of two sheet metal parts of substantiallyflat configuration. The one sheet metal part 9 is provided in one pieceabout its outer perimeter with a circumferential outer collar 11 whichprojects axially in the direction of the other sheet metal part 10.Arranged radially inwards of the collar 11 is the other sheet metal part10 and securely fixed about its circumference with the collar 11 throughlaser welding. The joint area between the collar and the other sheetmetal part 10 is located at the fee end of the collar 11. This ensuresthat the collar 11 is not inadmissibly deflected when exposed to aradial load. As shown in FIG. 1a, the outer surface area of the collar11 may also be convexly curved.

Both sheet metal parts 9, 10 are each provided in one piece about theirinner circumference with a circumferential inner collar 12, 13, withboth free ends of these collars 12, 13 confronting one another andbounding a hub opening 14 for receiving a carrier (not shown). Cavities15 are defined between both sheet metal parts 9, 10.

FIG. 3 shows a further friction wheel according to the invention whichdiffers from the one shown in FIG. 2 substantially in that both sheetmetal parts 9, 10 are each provided in one piece about their innercircumference with a circumferential inner collar 17, 18, having freeends which face away from one another, The one sheet metal part 9has—like the sheet metal part 9 of FIG. 2—several depressions 16 evenlyspaced about the circumference and jutting out in the direction of theother sheet metal part 10 for bearing against the other sheet metal part10. Each depression 16 is securely fixed to the sheet metal part 10through spot welding. The afore-mentioned bolt (not shown) can becompletely eliminated here as a radial bearing 18, 19 is provideddirectly between the collars 17, 18 and the carrier 7 for support of thefriction wheel 6 with respect to the carrier 7. Disposed on the innercollar 17 is a radial deep groove ball bearing 19, and disposed on theinner collar 18 is a radial needle bearing 20. The outer circumferentialsurface of the inner collar 18 is also a raceway 21 for needles 22 ofthe radial needle bearing. The collar 17 is formed on Its outer surfacearea with a ball groove 23 for rolling of balls 24 of the radial deepgroove ball bearing 19.

FIG. 4 shows a top view the friction wheel according to the invention ofFIG. 3 to clearly show the depressions 16 spaced about thecircumference.

What is claimed is:
 1. A toroidal transmission with infinitely variabletransmission ratio, comprising: a driving first disk; a driven seconddisk; and at least one friction wheel disposed between the first andsecond disks and rotatably mounted to a swingable carrier, said frictionwheel having a circumferential friction surface for interaction withconfronting end faces of the first and second disks, wherein thefriction wheel is made of two sheet metal parts interconnected outsidethe friction surface to form a cavity therebetween and defining apartition plane which is disposed substantially transversely to arotation axis of the friction wheel, wherein the sheet metal parts havea disk-shaped configuration, one of the disk-shaped sheet metal partsprovided in one piece about its outer circumference with acircumferential outer collar which has an outer surface area definingthe friction surface.
 2. The transmission of claim 1, wherein both sheetmetal parts are welded together at formation of a welding seam locatedoutside the friction surface.
 3. The transmission of claim 1, whereinthe other one of the disk-shaped sheet metal parts is disposed withinthe outer collar and securely fixed to the outer collar.
 4. Thetransmission of claim 1, wherein the outer surface area of the collar isconvexly curved.
 5. The transmission of claim 1, wherein the frictionwheel is provided with an inner collar in coaxial relationship.
 6. Thetransmission of claim 5, wherein each of the sheet metal parts has aninner circumference provided in one piece with a circumferential innercollar.
 7. The transmission of claim 6, wherein the inner collar of oneof the sheet metal parts and the inner collar of the other one of thesheet metal parts confront one another, with the inner collars boundingtogether a hub opening for receiving a bolt.
 8. The transmission ofclaim 6, wherein the inner collar of one of the sheet metal parts andthe inner collar of the other one of the sheet metal parts face awayfrom one another, and further comprising two radial bearings, one of theradial bearings disposed between one of the inner collars and thecarrier, and the other one of the radial bearings disposed between theother one of the inner collars and the carrier.
 9. The transmission ofclaim 8, wherein one of the inner collars has an outer surface areaforming a raceway for receiving rolling bodies.
 10. The transmission ofclaim 9, wherein the outer surface area has formed therein a ballgroove.
 11. The transmission of claim 1, wherein the friction wheel hasa circumference and is provided with depressions which are evenly spacedabout the circumference for stiffening the friction wheel.
 12. Thetransmission of claim 1, wherein at least one of the sheet metal partshas a circumference and is provided with depressions which are evenlyspaced about the circumference and jutting out in the direction of theother one of the sheet metal parts.
 13. The transmission of claim 12,wherein the depressions bear against the other one of the sheet metalparts.